Many commercially available natural fiber based composites have a matrix based on polyolefins, e.g., polyethylene, polypropylene, or both. Natural fiber based composites based on polyolefins have found much commercial success, particularly in the field of wood fiber containing composites, such as in residential decking applications. Even though the polyolefin based wood plastic composites (WPC) have been commercially successful, they still suffer some potential deficiencies. For example, it would be attractive to have improved flexural strength and modulus characteristics, as compared with may current materials.
Thermoplastic epoxy resin (TPER), also known as poly(hydroxyamino ether) (PHAE) is a thermoplastic resin based on epoxy chemistry, and is illustrated in U.S. Pat. Nos. 5,164,472; 5,275,853; 5,401,814 and 5,464,924, all incorporated by reference. Such material generally has a relatively high flexural strength and modulus—often much higher than typical polyolefins (i.e. polyethylene and polypropylene)—and has the added benefit of being melt processable at temperatures of 150 to 200° C.
Melt processing can be an important function in the manufacture of many composites, particularly when processing to include natural fibers or particles, such as those derived from plants (e.g., fibers based on cellulose, such as cotton, linen, jute, flax, ramie, sisal, hemp and wood). A number of commercially abundant natural fibers based on plants often decompose at temperatures greater than 200 to 220° C., limiting the upper processing temperature available to melt blend with thermoplastics and thus limiting the use of natural fiber blends with most engineering thermoplastics (e.g. nylon 6, nylon 6,6, PET, PBT, or others) which often melt process at temperatures of about 240° C. or higher.
TPER has been recognized as a potential candidate material for melt blends with natural fiber composites, which has the potential to easily produce a relatively high strength and high modulus reinforced composite material. For example, White et al (Plastics, Rubber and Composites, 2000 Vol. 29 No 8, p 395-400) report on an increase in tensile strength at break of more than 75% when a TPER sample is filled with 30 wt % wood flour (also, see generally, White et al, Adv. Matls., 2000, Vol. 12, No 23 p 1791-1800). An overview of wood flour as a filler in plastic materials is provided in Chapter 15 of “Functional Fillers for Plastics” (Ed. Xanthos; Wiley, 2005), authored by Clemons and Caufield, and entitled “Wood Flour”; hereby incorporated by reference.
The use of TPER as a matrix material by itself, however, poses practical constraints upon the useful application of the resulting composite material. It is desired for many applications to take advantage of the benefits that can be realized from the use of other polymeric materials, such as polyolefinic materials.
Simply blending TPER and a polyolefin with particles of a natural occurring biological material is not a predictable art, and does not necessarily lead to an attractive reinforced composite with high strength, high stiffness, or both. For one thing, TPER by itself generally is not chemically compatible with polyolefins. Simple melt blends of the two tend to produce materials that have low strength and tendency to delaminate. U.S. patent application 20070270515 A1, incorporated by reference, describes technology for chemically toughening TPER with polyolefins.
Accordingly, there remains a need in the art to find improved materials and ways to make and process them to take advantage of the abundance of naturally occurring biological materials.